Glowing jellyfish have lit the way to 2008's Nobel Prize in chemistry for one Japanese and two American researchers, pioneers in illuminating biological processes inside cells and behind diseases such as cancer and Alzheimer's.

Osamu Shimomura, 80, of the Marine Biological Laboratory in Woods Hole, Mass.; Martin Chalfie, 61, of Columbia University in New York; and Roger Tsien, 56, of the University of California-San Diego will split the $1.4 million prize, the Royal Swedish Academy of Science announced Wednesday.

"I didn't think I would win the prize," says Shimomura, a Japanese citizen. How does he feel about winning? "Not bad."

The three researchers received the prize for pioneering the use of Green Fluorescent Protein, which "has functioned in the past decade as a guiding star for biochemists, biologists, medical scientists and other researchers," the academy said in its award announcement. GFP, which is not used in humans, is injected or otherwise inserted into the bodies of laboratory animals. It glows under ultraviolet light, showing biological functions, infections and diseases as they happen in the animals.

"I don't think it was a surprise to anyone. This really fits the definition of Nobel science," says biochemist Richard Armstrong of Vanderbilt University in Nashville, editor of the journal Biochemistry. "It's used to an unbelievable extent in biology, even in high schools, and it's had a major impact."

In 1962, Shimomura and Princeton's Frank Johnson first isolated GFP in materials obtained by squeezing 10,000 jellyfish. His research showed that GFP, unlike other fluorescent proteins that required additives to shine, needed only ultraviolet or blue light to glow.

The glow is "very much like a black light in a 1970s disco," says Chalfie, who first heard of GFP at a 1988 seminar, where he decided to attach the gene for the glow to touch-sensing cells of nematode worms, creating a glowing creature featured on a 1994 cover of the journal Science. "We have the opportunity to follow the development of disease," such as the spread of cancer cells, Chalfie says. "This has become a very popular tool for fundamental biology."

Tsien has expanded GFP to a flurry of colors, such as plum, cherry, strawberry, orange and citrine, which allows researchers to explore multiple processes in lab animals at once. A 2007 Harvard study, for example, made cell types in mouse brains the colors of the rainbow.

"I like pretty colors and have always done so," Tsien says. "We knew this would be a tremendously powerful technique if we could make a direct link between molecular biology and something you could see."

The protein technology serves purposes beyond biology, such as tests for arsenic in well water and even glow-in-the-dark toys.

"This is why we fund basic research into fundamental life processes, things like nematode worms and glowing jellyfish," says Jeremy Berg, head of the National Institute of General Medical Sciences, which has funded all three researchers during their careers. "The prize shows the importance of tool development in science."